AC rattling at idle

[chipahoy]

need help. ac compressor makes rattling noise at idle (especially in drive). changed belt tensioner, no go. changed belt, no go. if i raise the idle a little with the throttle, the noise abates. is there any way to increase the idle speed, or do i have to live with this racket?

[amc49]

You can't alter the idle speed on a ECM controlled car, it's locked in software.

The clutch bearing of course could be dead or the faceplate front dampers could be shot. Could even be another bearing close to the a/c like an idler of some type.

[147jk]

Raising the idle just masks the problem and itself will cause other problems. Best to get the A/C fixed.. if you're certain that's what's rattling. BTW, even a computerized intake system will have a mechanical needle value to set the idle speed and mixture. Normally, you would not change it for the life of the car.

[amc49]

One can fake the idle higher by mechanical means but AGAIN, being locked in software the ECM WILL flag codes due to not being able to adjust back to the software idle speed number. AND doing that also creates hanging idle issues when the ECM again cannot pull the idle down, it has lost control of it. The mixture itself is absolutely off limits and cannot be changed other than by software and what closed loop is.